After part of the arches collapsed in the Church of St. Jean in Elbeuf (France’s Seine-Maritime region), the authorities decided to launch a major project to rebuild the damaged sections and strengthen the structure. The teams at Freyssinet’s Ile-de-France – Normandy office drew on their full expertise to reinforce the weakened plaster arches in this historical monument.

  • Name of the owner and client
    City of Elbeuf-sur-Seine (Seine-Maritime)
  • Delivery date of the project
  • Partners of the project
    RPL Normandie (lead contractor)

Bespoke lightweight reinforcements

Freyssinet’s teams were contracted to strengthen nine damaged arches in the chancel and ambulatory of the Church of St. Jean in the city of Elbeuf. A defining feature of the arches is that they had been made from plaster, which is a rare material for this type of structure. The downside is that they are more fragile than traditional masonry arches. A bespoke approach was needed to add greater strength. The upper reinforcing beams of the arches were made from reinforced resin concrete (15 m³). This material offered a number of important qualities, i.e. it was lighter than conventional concrete and avoided overloading the arch. It also prevented any chemical incompatibility between the plaster and the cement. In addition, resin concrete does not contain any water, meaning that there was no danger of corroding the reinforcements.

Consolidating the arches with carbon fibre

To maintain the structure’s lightweight design, the arches were consolidated using cross-strips of TFC carbon fibre fabric. The strips were first applied to the extrados and then the intrados of each arch according to a close lattice arrangement. Both surfaces were then connected with carbon braids that were fitted into the holes previously drilled through the arch. Forming a “tassel” at each end of the cross braids, the fibres were deployed and linked to the fabric strips with epoxy resin. This reinforcement system ensured that the composite reinforcements were securely sealed in the arches, all of which have now been strengthened.

Key figures of the project

Total length of the TFC carbon fibre fabric used (km)
Number of braids used
Total surface area of the nine plaster arches requiring repairs (m²)

A logistics process geared towards the constraints of a historical monument

Access to the work areas represented one of the main challenges with this project. Since they were working on a historical monument, our teams had to comply with each and every requirement laid down by the Chief Architect of Historical Monuments, who was also the project manager. For example, changing the church’s layout, even temporarily, was out of the question. The teams could only create a single access opening for all nine arches, meaning that they had to use a narrow spiral staircase without a landing. When it came to the materials, the fresh resin concrete was poured into buckets and winched through the chimney that had been designed for fitting the bell. The buckets were then hung from a cable stretching from either end of the 80-metre church. This ingenious zip line system was also used to remove the rubble from the demolition work.